1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly to a method for managing user equipment capabilities in a wireless communication system.
2. Discussion of the Related Art
Typically, a 3rd Generation Partnership Project (3GPP) mobile communication system based on a Wideband Code Division Multiple Access (WCDMA) radio access technology has been widely developed throughout the world. A High Speed Downlink Packet Access (HSDPA) defined as a first evolution step of a WCDMA technology provides the 3GPP system with a high-competitiveness wireless access technology in the near and mid-term future. However, the number of requests and expectations of users and enterprisers is rapidly increasing, and the wireless access technology is being intensively developed, such that there is needed a new or improved technology of the 3GPP in order to implement a high competitiveness in the future. For example, the cost for each bit, the increase of service availability, an adaptable use of frequency band, a simple structure, an open-type interface, and appropriate power consumption of user equipment (UE) are needed for the 3GPP.
In order to manage the mobility of a user equipment (UE), an EPS Mobility Management-REGISTERED (EMM-REGISTERED) status and an EMM-DEREGISTERED status are defined in the 3GPP LTE system. The EMM-REGISTERED status and the EMM-DEREGISTERED status are applied to a Mobility Management Entity (MME). The user equipment (UE) is initially in the EMM-DEREGISTERED status, and carries out an ‘Initial Attach’ procedure to access a network, such that it is registered in this network. If this ‘Attach’ procedure has been successfully carried out, the UE and the MME become enter the EMM-REGISTERED status.
In order to manage a signaling connection between the UE and the EPC, an EPS Connection Management (ECM)-IDLE status and an ECM-CONNECTED status are defined. The above-mentioned statuses are applied to the UUE and the MME. The UE of the ECM-IDLE status is in the ECM-CONNECTED status when it makes a RRC connection with an E-UTRAN. If the MME of the ECM-IDLE status makes a S1 connection with the E-UTRAN, it becomes enter the ECM-CONNECTED status. If the UE is in the ECM-IDLE status, the E-UTRAN has no context information of the UE. Therefore, the UE of the ECM-IDLE status carries out an UE-based mobility procedure (e.g., a cell selection or a cell reselection) without receiving a command from the network. Otherwise, if the UE is in the ECM-CONNECTED status, the UE mobility is managed by the network. If the UE is in the ECM-IDLE status and the UE's location recognized by the network is changed to another UE location, the UE performs a Tracking Area Update procedure, such that it informs the network of the UE's location.
If a connection between a base station (or eNode-B) and a user equipment (UE) is established, the base station (BS) requests user equipment (UE) capability information from the user equipment (UE), such that it can establish radio resources for the user equipment (UE). In order to allow a network to manage the UE (e.g., a support of UE mobility), the UE capability information is needed. The UE capability information may include a variety of information for managing/operating radio resources of the UE, for example, a power control associated information, code resource information, encryption-associated information, and a PDCP-associated capability. The UE capability information may include a radio access technology (RAT) supported by the UE.
FIG. 1 is a conceptual diagram illustrating a conventional delivery flow of the UE capability during the ‘Attach’ process of the UE. Detailed descriptions of FIG. 1 are as follows.
First, the UE establishes a Radio Resource Control (RRC) connection. Namely, the UE performs the RRC connection establishment by sending a message with a Random Access Channel (RACH) preamble to the eNode-B (eNB), receiving an initial allocation from the eNB, and sending a RRC CONNECTION SETUP message to the eNB. If the RRC connection has been successfully established, the UE transmits a RRC CONNECTION COMPLETE message to the eNB. The UE includes a NAS ‘Attach Request’ message in the RRC message.
Second, if the eNodeB (eNB) receives the RRC connection complete message, the eNB transmits a S1 control message (i.e., initial UE message) having the NAS message (Attach Request) to the MME.
Third, in response to the ‘Attach Request’ message, there is an authentication process between the UE, the eNB and the MME, including a step where the MME transmits the S1 control message (i.e., Initial Context Setup Request) to the eNode-B (eNB).
Fourth, the eNode-B (eNB) receives the ‘Attach Accept’ message from the MME.
Fifth, the eNode-B (eNB) carries out an initial security activation process including sending a SECURITY MODE COMMAND message to the UE and receiving a corresponding SECURITY MODE COMPLETE message from the UE.
Sixth, the eNode-B (eNB) receives UE capability information from the UE by sending a UE CAPABILITY ENQUIRY message to the UE and receiving a corresponding UE CAPABILITY INFORMATION message from the UE.
Seventh, the eNode-B (eNB) performs a RRC Connection Reconfiguration procedure using the received UE capability information, such that it acquires the latest UE capability from the UE. This includes sending a RRC CONNECTION RECONFIGURATION message with a NAS: Attach Accept datum to the UE, and receiving a corresponding RRC RECONFIGURATION COMPLETE message from the UE.
Eighth, the eNode-B (eNB) transmits a SI control message (Initial Context Setup Response) having the UE capability information to the MME.
With the conventional process shown in FIG. 1, the UE capability is transferred to the network whenever the UE establishes the RRC connection. However, as the UE supporting various wireless access technologies is introduced to the market and the UE function becomes more complex, the UE capability is gradually increasing. In view of increasing UE capability and increasingly large UE capability information sizes, the conventional method for transferring a large amount of information to the network whenever the RRC connection is established unavoidably encounters unnecessary consumption of radio resources.